refactor: replace inline HERMES_HOME re-implementations with get_hermes_home()

16 callsites across 14 files were re-deriving the hermes home path
via os.environ.get('HERMES_HOME', ...) instead of using the canonical
get_hermes_home() from hermes_constants. This breaks profiles — each
profile has its own HERMES_HOME, and the inline fallback defaults to
~/.hermes regardless.

Fixed by importing and calling get_hermes_home() at each site. For
files already inside the hermes process (agent/, hermes_cli/, tools/,
gateway/, plugins/), this is always safe. Files that run outside the
process context (mcp_serve.py, mcp_oauth.py) already had correct
try/except ImportError fallbacks and were left alone.

Skipped: hermes_constants.py (IS the implementation), env_loader.py
(bootstrap), profiles.py (intentionally manipulates the env var),
standalone scripts (optional-skills/, skills/), and tests.

hermes_cli/commands.py

@@ -294,10 +294,8 @@ def _resolve_config_gates() -> set[str]:
         return set()
     try:
         import yaml
-        config_path = os.path.join(
-            os.getenv("HERMES_HOME", os.path.expanduser("~/.hermes")),
-            "config.yaml",
-        )
+        from hermes_constants import get_hermes_home
+        config_path = str(get_hermes_home() / "config.yaml")
         if os.path.exists(config_path):
             with open(config_path, encoding="utf-8") as f:
                 cfg = yaml.safe_load(f) or {}